Yahya Sinwar is increasingly fatalistic, has blocked a cease-fire deal and, so far, been frustrated that Hezbollah and Iran have not come to his aid, officials said.

After his release, Sinwar rose in the Hamas ranks. In 2017, he became the Hamas leader in the Gaza Strip. Then after Ismail Haniyeh was killed in a suspected Israeli attack in Tehran this year, he became the chairman of the Hamas Political Bureau, or the group's de facto leader.

In an airstrike three months ago, Israel’s military killed Rawhi Mushtaha, a senior Hamas leader, along with fellow commanders Sameh Siraj and Sameh Oudeh. Mushtaha was Yahya Sinwar’s key associate, managing Hamas' civil governance and security operations in Gaza.